Investigation On Mechanical Properties And Durability Of Lignin Calcium Graphene On Cement-based Materials

Cement composite is the most extensively used engineering material.However,it has limited structural applications due to some significant disadvantages such as poor flexural strength and electrical conductivity.The emergence of graphene-based nanomaterials provides new ideas for solving this problem.Among them,graphene oxide(GO)and thermally reduced graphene oxide(TRGO)are the most potential nanocomposites to blend into based materials.Both GO and TRGO are graphene-based nanomaterials,which have large specific surface area,ultra-high strength and excellent conductivity.However,GO and TRGO are very easy to accumulate in the cement hydration environment of high calcium and alkali,so that the key to achieving the effect of strengthening and toughening cement-based materials is to improve the dispersion performance of GO and TRGO in cement hydration media.At present,the study on GO or TRGO mixed with cement-based materials which mainly used polycarboxylate superplasticizer as the dispersant of GO and TRGO.This paper investigated that calcium lignosulphonate(lignin calcium)with many benzene ring ring structure is used as auxiliary dispersant to collaboratively disperse GO and TRGO in saturated calcium hydroxide solution,and the effects of highly dispersed GO and TRGO on the mechanical property and durability of cement-based materials.The results are as follows:(1)The dispersion of GO and TRGO in the calcium hydroxide(CH)solution was tested by ultraviolet-visible spectrophotometer(UV-vis),it was found that when the mass ratio of lignin calcium to GO is 3:1 and the mass ratio of lignin calcium to TRGO is 5:1,the dispersion effect of GO and TRGO in saturated CH solution is significantly improved.(2)Both Zetasizer Nano particle size analyzer and Atomic Force Microscopy(AFM)were used to characterize the dispersion of GO and TRGO dispersion liquid.It was found that the dispersing effect of the dispersion solution after adding extra lignin calcium was greater than that of PC alone dispersing GO and TRGO,and the dispersing solution presented the best state when the mass ratio of lignin calcium to GO was 3:1and the mass ratio of lignin calcium to TRGO was 5:1.(3)Mechanical properties: when the amount of 0.03% GO by weight of cement and the mass ratio of lignin calcium to GO is 3:1,the 3 day compressive strength is increased by 22.5% compared to the PC alone dispersed GO cement mortar test piece(the contrasted test piece),the flexural strength increased by 40.9%;the 28-day compressive and flexural strength increased by 17.2% and 22.1% respectively.When the amount of TRGO is 0.07% and the mass ratio of lignin calcium to TRGO is 5:1,the3-day compressive strength is increased by 25% and the flexural strength is increased by 31% compared to the PC alone disperses GO specimen(the contrasted test piece);the 28-day compressive strength increased by 25% and flexural strength increased by28%.The Scanning Electron Microscope images(SEM)of cement mortar and cement paste show flower-like microstructure,which confirmed that GO and TRGO with good dispersion can adjust the microstructure of cement hydration products and make the hydration products grow better,fill some pores.In addition,GO and TRGO can act as stress concentration points to delay the formation and development of cracks.(4)Durability test: When the GO content is 0.03% of cement mass,lignin calcium content is 0.09% or TRGO content is 0.07%,lignin calcium content is 0.035%,the erosion resistance of mixed cement showed the best condition in freeze-thaw cycle test and sulfate drying-wetting cycle test.It shows that lignin calcium collaboratively disperse GO and TRGO that can make cement mortar resist part of external erosion,compact internal structure,and improve the durability of cement-based materials.